Cholera is an infectious disease that spreads in countries without clean drinking water or adequate sewage disposal. The bacterium
causing the disease was identified in 1884. How it causes disease
was discovered almost 100 years later.

A toxin
produced by the bacterium changes the G-proteins
in cells lining the intestine.
The G-proteins become "stuck" in the activated—or turned on—state.
They can't turn themselves off as they do when normally regulated.
The effect is that water is pumped continuously out of the cells into
the intestines, causing dangerously severe diarrhea.

What
Causes CholeraNormally, both the receptor and the
amplifier span the membrane. The G-protein sits on the inner
surface of the membrane. This current view is a little different
from Rodbell's original model. In a person with cholera, the
G-protein is stuck in the "on" position-next to the AC moleculeImage:
Courtesy of NIDDK